The invention concerns a double belt press, comprising two continuous steel belts revolving in directions opposite to each other. Mutually facing sides of the belts are pressed against each other and against material conducted therebetween, by means of temperature controlled press plates. The belts are guided along the press plates by means of roller chains which are speed-coordinated with the press plates.
Double presses of this type are known (see German AS No. 27 29 559). In those known designs, heated press plates are usually provided so that, for example in the continuous production of pressboard plates, not only the necessary pressure, but also the required temperature may be applied. The necessary transfer of heat from the press plates to the steel belts and from there to the material to be treated is effected by rolls revolving between the press plates and the steel belts and guided on the roller chains.
It is also known to provide different zones of treatment of the above-mentioned type in double belt presses so that for example, certain zones may be at different temperatures. There are, however, certain production processes where it is desirable not only to provide zones with different temperature ranges in sequence, but wherein it is necessary to effect subsequent manufacturing steps whereby sudden rises or drops in temperature are required. Such changes in temperature are not feasible with the known designs of double belt presses. It is hindered essentially by the mass of the revolving roller chains which is very large compared with the mass of the revolving steel belts and the thin layer of material in between. The individual roll links of the roller chains do transfer the requisite amount of heat to the material from the press plates or inversely from the material to the plates, but because of the temperature inertia created by their large mass, they are unable to effect sudden steep variances in temperature.
Installations have been proposed wherein a substantial amount of heat may be removed from the material very rapidly for example by means of an intensive spray cooling of the rear side of the revolving steel belts. Such heat transfer means, acting possibly in both directions, prevent, however, the application of high pressures, because the revolving steel belts must be necessarily guided on pressure elements, which with existing materials cannot be rendered sufficiently frictionless to permit their practical use without the insertion of roller chains.
It is, therefore, an object of the invention to provide a double belt press which enables the material to be treated to be exposed both to high pressures and to large, abrupt changes in temperature.